The energy-per-bit efficiency has become the ultimate capacity limiting factor for future routers and data center networks. People have turned to optics for solution. If the switching can be done optically, the E/O and O/E conversions inside the switch will disappear and tremendous power saving can be achieved. As optical switching devices, AWGRs (Arrayed Wavelength Grating Router) have many advantages. They are passive and consume little or no power. They allow WDM signals and have high per-port capacity. The only problem is that they are limited in size. How to design an AWGR-based scalable switch is an important issue for future datacenters and routers.
One such design is the ASA switch architecture presented in U.S. Pat. No. 9,497,517 and in the paper C-T Lea, “A Scalable AWGR-Based Optical Switch,” IEEE Journal on Lightwave Technology, Vol 33, No 22, November 2015, pp. 4612-4621. This architecture contains an optical switching fabric plus an electronic scheduler. The optical switching fabric consists of three switching stages: AWGRs (Arrayed Wavelength Grating Router), space switches, and AWGRs. It is named ASA for the technologies used in the three stages. The sizes of the AWGRs and the optical space switches used in the architecture are N×N and there are up to N AWGRs in the first and the third stages. This makes the maximum port number in the ASA architecture N2. Each port can send up to N packets of different wavelengths simultaneously. The total capacity of the switch is close to (N3×bandwidth of each wavelength channel).
Although the ASA switch architecture can expand the port count from N to N2, it has two limitations. (a) It still needs an electronic scheduler to coordinate transmissions from all ports. This can be a potential bottleneck. (ii) It performs poorly under certain traffic patterns. In this patent, a modified version of the ASA architecture is presented to fix these problems. The new switch does not need an electronic scheduler and performs equally well under any traffic load.